Selective potentiators of the metabotropic glutamate receptor subtype mGluR5 have exciting potential for development of novel treatment strategies for schizophrenia and other disorders that disrupt cognitive func-tion. The latest generation of selective mGluR5 potentiators is based on the lead compound CDPPB and features systemically active compounds with long half-lives that cross the blood-brain barrier. A high-throughput screen (HTS) for mGluR5 potentiators at Vanderbilt's screening center revealed a large and diverse set of about 1400 substances (1% hit rate) whose activity was validated in independent experiments. A previous exploratory research grant Novel Schizophrenia Therapeutics by Virtual High-Throughput Screening (R21 MH082254) enabled testing of 813 compounds predicted through cheminformatics. 252 of these compounds were confirmed as active PAMs equaling an enrichment of >30 when compared with the original screen. The present proposal seeks to leverage these proof-of-principle results for the development of a tailored cheminformatics framework for drug discovery of allosteric modulators of brain GPCRs, apply these tools to inform an existing therapeutic discovery program of mGluR5 potentiators at Vanderbilt University, and disseminate the methods broadly through the NIH molecular libraries program. The central hypothesis of this proposal is that the complex relationship between chemical structure and biological activity of mGluR5 potentiators observed in this HTS can be used to generate a pharmacophore of the mGluR5 allosteric site. This map of steric and electronic features necessary for optimal interaction of modulators with mGluR5 will not only inform our understanding of the allosteric modulation of brain GPCRs. The methods proposed overcome limitations of present cheminformatics techniques by enabling identification of novel chemotypes through virtual screening (scaffold hoping), and allowing design of focused libraries in hit-to- lead optimization of novel schizophrenia therapeutics. The generalizbility of the approach will be tested through application on negative modulators of mGluR5, a potential novel treatment strategy of fragile X syndrome, a CNS disorder associated with autism spectrum disorders (ASD) among multiple other symptoms. The developed applications will be made freely and readily accessible for academic research. The employed QSAR models require no crystal structure of the target brain GPCR. Hence the method can be readily applied to membrane proteins-such as GPCRs-which are target of 40-50% of modern medicinal drugs.